Ringing tone

Ringing tone (audible ringing, also ringback tone) is a signaling tone in telecommunication that is heard by the originator of a telephone call while the destination terminal is alerting the receiving party. The tone is typically a repeated cadence similar to a traditional power ringing signal (ringtone), but is usually not played synchronously. Various telecommunication groups, such as the Bell System and the General Post Office (GPO) developed standards, in part taken over by the European Telecommunications Standards Institute (ETSI) and other standards bodies. With modern cell phone and smartphone technology ringing tone can be customized and even used for advertising. When a telephone user initiates a telephone call, typically by dialing or selecting a telephone number on a telephone, the progress or status of the call attempt is indicated to the user audibly by several types of call progress tones. For example, during the period of routing the call across the public switched telephone network (PSTN) the call may encounter congestion on a particular link. If this cannot be automatically resolved, the calling user receives the congestion tone, also called reorder tone. If the called station is already busy and cannot accept a second call via call waiting, the calling party is alerted with a busy signal. When the call routing is successful and the receiving telephone is not already in a call, the destination telephone receives an electrical signal, called power ringing, or the ring tone, to alert the recipient of the incoming call. During this period of alerting, the caller also receives a distinctive signal, audible ringing, also called ringing tone. Audible ringing is typically a repeated burst of tone that is typically not synchronous with the cadence of the power ringing signal at the destination. It is usually generated in the switching system closest to the calling party, especially when under the control of strict implementations of Signalling System No. 7 and the Customized Application of Mobile Enhanced Logic (CAMEL) signaling system.